Internal combustion engine (ICE) was invented in 1876. Its typical four-stroke reciprocal piston configuration is still the primary engine format today. Modern gasoline ICE has 25% to 30% fuel conversion efficiency. This means that only 25% to 30% of the energy in the consumed fuel is converted into mechanical power, while the rest is lost through friction and heat. Due to millions of ICE currently in use worldwide, the improvement in ICE fuel conversion efficiency will have huge impacts on energy consumption, fuel economy, fuel reserve, dependency on foreign oil, and the environment.
ICE causes air pollution by discharging emission gases. The emissions from millions of vehicles combine with sunshine and moisture to produce greenhouse effect. Although governments continue to pass through anti-pollution laws, automobile manufacturers are designing new vehicles with improved emissions, and oil companies are changing their formulations to burn more clearly, dangerous emissions from vehicles still remain an environment problem.
One of the major content of ICE exhaust is carbon dioxide, which contributes to global warming. The increasing density of carbon dioxide traps the solar heat, causing the atmosphere temperatures to rise, leading to violent weather patterns and the melting of polar icecaps.
The best way to reduce carbon dioxide emissions is to burn less fossil fuel by using engines with higher efficiency. Even when we enter the era of biofuels and/or alternative fuels, or hydrogen fuels finally, increasing fuel conversion efficiency and reducing fuel consumption is still a significant strategic solution, because the higher the fuel costs, the higher the engine efficiency is expected.
It is believed that much of benefit would come from fuel efficiency improvement. A 10% efficiency improvement in vehicle performance would save over $10 billion of US dollars and reduce emissions of carbon dioxide by 140 million tons per year. A 20% efficiency improvement could reduce foreign oil used today by one-third. Environmentalists claim that increasing the average vehicle mileage to 40 MPG would save more oil than we get from Persian Gulf imports, the Arctic Wildlife Refuge and California offshore drilling combined. Consumers would save billions of dollars in fuel costs. Reduction in emissions would be in the hundreds of millions of tons per year, and dependency on foreign oil would be drastically reduced.
Therefore, a new kind of heat engine, with much higher fuel conversion efficiency, is desired that addresses the immediate and specific needs of reducing fossil fuel consumption, reducing greenhouse gas discharge and reducing combustion exhaust emissions.
Despite immense efforts over the past 100 years, engine fuel conversion efficiency has no major improvement both theoretically and practically. Around academic field of ICE, Homogeneous Charge Compression Ignition (HCCI) is a well-known theory that it was referred as a hopeful ICE solution, and was being studied extensively. But little progress was achieved during the past decades, nor has its practical utilization been found. Until recently, top US academic authority turns to promote Heterogeneous Combustion and Staged Combustion adversely. This could be a fact that fully turns HCCI down. Wondering back and forth theoretically, more fails than success, ICE has suffered the lack of significant progress in practice over the past centenary.
However, it is not impossible to improve fuel conversion efficiency of heat engine. During 19th century, a steam engine with an efficiency of 6% to 7% was referred as high efficient. Not until the middle of 20th century, when steam engine was almost being replaced by ICE, a French mechanical engineer called Andre Chapelon was able to obtain 13% efficiency by thermodynamically modifying steam engine with compound cylinders and super-reheating. This could be a historical fact that the engine efficiency can be doubled. Modern late 20th century power plants utilizing combined heat-work conversion cycles could yield an overall thermal efficiency as high as 60%, where different working fluids drive different power cycles, obtaining a combined thermal efficiency from each of the individual power cycles. This could be another evidence that engine efficiency could be doubled from the current 30% from conventional ICE. All of these could be the clues that lead to engine fuel conversion efficiency improvement. Based on such an inventive thinking, we could foresee that the challenge and chance of the 21st century engine revolution is waving to us.